If you actually calculate the volume of these bags, they are 440 ish. The box says 550+ as if you over fill them at all, you are going to get more weight than what it says online. It is just a given that they stretch and fill up whatever space they have available.

I have gotten 450 lbs. out of them before but I still consider them to be 400 lb sacs in most cases. You can fill them extremely full but I start to wonder what kind of stresses are on those seams. With that said we did not inflate the capacity on the Wakemakers product page.